Related U.S. Pat. No. 4,919,153 is concerned with a method and apparatus for removing the cement mantle used to secure a prosthetic appliance within a bone cavity and, more particularly, is concerned with a technique wherein a new mass of cement is adhered in place within the mantle and a pulling tool is then employed to remove the mass and the mantle as a unit. Application Ser. No. 467,724 and application Ser. No. 467,742 are concerned with improvements wherein the cement mantle and newly injected mass of cement are removed in increments to avoid the severe stresses which are sometimes encountered in removing the cement mantle and newly injected mass of cement as a single unit. Application Ser. No. 467,724 is particularly concerned with an improvement of the latter type wherein a plurality of pulling tools of different lengths are successively screwed into the newly injected mass of cement to affect the incremental removal of the mantle.
The apparatus and method of application Ser. No. 467,724 functions well, except for the possibility of stripping out the threads formed in the cement mass into which the pulling tools are threaded. The enlarged diameter shoulders on the pulling tools of the latter application are designed to give the surgeon tactile indication that the pulling tool has been threaded into the cement plug completely. In practice, however, it is difficult for the surgeon to feel the difference between a pulling tool that is fully threaded into the cement plug, and one that has been overtightened. A T-handled wrench is used to thread the extraction rod into place, and substantial torque can be developed during placement. Overtightening of the extraction rod can cause the threads formed in the new cement to strip out, thus rendering the system useless.
One method of dealing with the thread stripping problem encountered in using the pulling tools of application Ser. No. 467,724 is to count the number of turns corresponding to the desired depth of pulling tool insertion. While this method works, it is slow and cumbersome. It also requires that the number of turns be calculated in advance and carefully counted as the tool is threaded into place.